i'm a 12th grade student and our school has a safe competition, which means we need to build a safe that you can open with the laws of physics. we have a pendulum and we don't want it to move if someone is tilting the safe, so we want to make a "defense mechanism" against it, so i want to detect if someone moved the circuit and i have a mercury sensor. the circuit i want to build shuts off an other circuit powered by a 9 volt battery that contains a single electric motor for 3 seconds if someone moved it. how does the circuit looks like? i don't have any size constraints, i can store it and make it as big as needed.
closed as not constructive by Kevin Vermeer Apr 12 '12 at 13:43
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Instead of having a separate movement detector why not build it into the pendulum? A spring like this will short to the pendulum when movement is detected, but if the spring is supple enough will not hinder the movement. As long as the safe is being moved the 'switch' will be closed.
The detector circuit could be constructed from a 555 timer and a relay.
The 555 timer configured for retrigerable monostable operation:
The 555 can drive a small relay. Choose one a relay that is normally 'on' then when the circuit triggers it will turn off for the chosen time delay.